Radishes grow quickly and children like their spicy taste and crunchy texture.
Every school garden should have some sprinkled in with other greens or dedicate a small patch where students can witness the stages of growth and experience the delight of harvesting them from the ground.
Radishes have a wide range of characteristics - spicy to mild, round or oblong, big or small, reddish-purple to rosy pink, black, pure white or even green. This guide describes many varieties. https://www.gardeningknowhow.com/edible/vegetables/radish/types-of-radishes.htm
Radishes are a cool season crop. Direct sow the seed in garden beds in the Fall and/or early Spring in a sunny location, according to the packet directions.
The toilet paper method is described here, also a great tip for covering seeds to protect from birds For more tips for planting small seeds see https://www.youtube.com/watch?v=S9ZmyqmgSB4.
Most radishes are planted in rows ½” deep and a couple inches apart. Since the seeds are quite small and hard to see on the soil, I like to use the toilet paper planting method (you’ll definitely get some giggles!) so students can see where the seeds fall and use popsicle sticks to space them properly for good germination.